A joint between two structural members requires a connecting point and a manner of connecting the two members. Depending upon the type of joint and its requirements for operation, the joint may be either fixed or movable. In the case of a movable joint, the connection should be flexible. This flexibility allows the joint to operate within a defined range-of-motion. When unrestricted range-of-motion of a joint is not desired, the manner of connection must provide at least some resistance to the members.
The development of modern prostheses and artificial limbs provides a specific example of these requirements in practice. Any artificial limb containing a joint must travel within a natural range-of-motion in order to approximate human anatomy and thus allow the most utility possible. While utility may be of primary concern, the limitations of the rest of the human body cannot be ignored. For this reason, any artificial joint must also provide resistance to unrestricted motion.